1. Field of the Invention
The present invention relates to an atomic absorption spectrophotometer and, more particularly, to an atomic absorption spectrophotometer with an arrangement for flame system-flameless system switching in the atomizing means.
2. Prior Art
As atomizing method in atomic absorption spectroscopic analysis there are known two alternatives of flame system in which atomizing is done by burning a sample in a burner and flameless system in which atomizing is done by flowing a high-amperage current through a graphite tube of an electric furnace. In order to enable switching of these two atomizing systems with a single atomic absorption spectro-photometer, Hidehisa Nishigaki, one of the present inventors, already proposed an atomic absorption spectro-photometer provided with switchable atomizing means of each system (See Japanese Laid-open Patent Publication No. 61-286737.)
The flame system with its low sensitivity is suited for analysis of samples high in concentration, while the flameless system with its high sensitivity is recommended for analysis of samples low in concentration. These two systems are different in sampling method. In the flame system the sample solution is sucked via tube into an atomizer. In the atomizer the sample solution is mixed with a fuel gas and a combustion improving gas, the mixture is led from a burner chamber to a burner head and there it is atomized in a flame. Since the sample is sucked into the burner chamber continuously, the quantity of the sample is required to be quite large. Meanwhile, in the flameless system a trace amount of the sample (several tens .mu.l) is injected into a sample inlet tube made of graphite and the graphite tube is then heated to atomize the sample.
As measurement is made by the flame system, it sometimes occurs that the sensitivity attainable is insufficient depending on the sample's concentration. And, should it be the case, it is necessary to do another measurement by the flameless system. During measurement by the flameless system, it also occurs that the sample's concentration is so high that the limits represented by the analytical curve are exceeded. Should it be the case, it is necessary to do re-measurement with the sample diluted properly or do it later by the flame system.
When measurement is taken with the flame system and the flameless system being switched, immediate re-measurement with the same sample is infeasible even by switching the atomizing method in case of an atomic absorption spectrophotometer provided with atomizing means of the flame system and the flameless system for the sampling method is different for each type of atomizing means.
With the atomic absorption spectrophotometer, too, adoption of an auto-sampler for automatic injection of a sample is conceivable. It is, however, infeasible to use a common auto-sampler for both systems if a suction type of sampling method is adopted for the flame system and a sampling method in which a trace amount of sample is dripped is adopted for the flameless system.